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• Over-excavation of the initial 10,000 gallon tank removal cavity (from 1990) and segregation of soil affected by BTEX from unaffected excavated soil, Continued over-excavation on the basis of analytical testing by Transglobal Environmental Geochemistry, a mobile laboratory facility, ' • Completed the removal of approximately p 600 cubic yards of soil (affected by TPHg and ' BTEX) and extended the tank pit to a depth of approximately 32 feet below grade, • Transported the affected soil to Remco in Richmond, California for recycling purposes, ' • Collected confirmation soil samples from the tank pit sidewall and base and submitted them to WESTON's analytical facility in Stockton for purposes of verifying mobile laboratory fresults ' • Backfilled the tank pit/excavation with approximately 870 cubic yards of pea gravel to within 5 feet of grade The pea gravel was covered with a low permeability ("geomembrane") liner and unaffected soil was placed on the liner to surface grade The ' backfilled area was compacted and the area was covered with crushed rock The WESTON depiction of the former tank excavation (plan view) and location of confirmation samples collection points is provided in Appendix I A copy of the WESTON Confirmation Soil Sample Analytical Results is also enclosed The limits of detection for BTEX compounds ranged from 2 4 to 26 parts per billion (ppb) 3.3 ESTIMATES OF AFFECTED SOIL VOLUMES REMAINING 3 3.1 Former Tank Pit Area An estimate of the residual mass of chemicals in the Site soil column was calculated based on the volume of a cylinder of forty feet in diameter extending from the base of the former tank-pit excavation to the current groundwater levels Data reported by WESTON indicated that excavations in the former tank pit extended for a depth of approximately 32 feet below grade and was Iapproximately 30 feet by 30 feet in areal dimension We estimated a cylinder volume of soil extending from 32 to 72 feet below grade was considered to be a conservative volume for developing estimates of residual chemical mass in soil, related to a gasoline product loss from the former UST's An estimate of total chemical mass for benzene, toluene, xylenes, ethylbenzene, and 1,2 DCA was calculated as presented in Table 2 based on the maximum detected value in exploratory soil bonngs by SECOR (SECOR, September 30, 1994) and/or excavation confirmation soil samples analyzed by WESTON (WESTON, May 14, 1993) The results of these calculations ISECOR International Inc (SECORO) CRC Environmental Risk Management Inc N0026 OOI Ol add 9 November 30 1994 I